Sleep mask



FIG. 1 is a elevated front perspective view of the design;

FIG. 2 is a elevated rear perspective view thereof;

FIG. 3 is a elevated front, side perspective view thereof;

FIG. 4 is a elevated rear, side perspective view thereof; and,

FIG. 5 is a front view of the design in extended state of a sleep mask. 

The ornamental design for sleep mask, as shown and described. 